This application is generally related to a number of other applications which each define suspension control systems. Each of these related applications has been given an application number as listed below:
______________________________________ NAME APPLN. # FILING DATE ATTN-DOCKET # ______________________________________ Tsutsumi 07/520,185 May 8, 1990 78879CDCTY00 Hara 07/535,194 June 7, 1990 76044/U3-900 Tsutsumi 07/580,387 Sept 11, 1990 81282/CDC/TY ______________________________________
(1) Field of the Invention
The present invention generally relates to a suspension control system, and more particularly to a suspension control system for controlling a damping force of a variable damping force type shock absorber on the basis of a running condition of a vehicle.
(2) Description of the Related Art
There is previously known a suspension control system in which the damping force of a shock absorber is controlled on the basis of the rate of change of the damping force. When the change rate of the damping force exceeds a predetermined value, that is, when the change rate changes abruptly due to a rough road surface or braking, the damping force with respect to a movement of the shock absorber is rapidly changed to a small level, so that the control response characteristics of the shock absorber are improved.
There is also known a suspension control system in which an adjustment reference value provided for obtaining the damping force change rate used for changing the setting of the damping force is altered on the basis of a driving condition, such as a vehicle speed, so that riding comfort is improved (see Japanese Laid-Open Patent Application No. 64-67407).
The conventional suspension control system proposed in the above-mentioned Japanese Application has an advantage in that the damping force is rapidly changed in accordance with the road surface condition so that good riding comfort is obtained. However, there is room for improvement in riding comfort in a case where the vehicle is continuously running on a flat road surface or a rough road surface for a predetermined time or longer. When the vehicle is continuously running on a flat road surface, the shock absorber is controlled so that the damping force thereof is maintained at a large level and thus the suspension is maintained in a hard state. In this state, the driver or passenger will feel the existence of a small roughness in the road surface. On the other hand, if the vehicle is continuously running on a rough road surface, the shock absorber is controlled so that the damping force thereof is continuously maintained at a small level and thus the suspension is continuously maintained in a soft state. This state deteriorates the road holding ability of the vehicle and causes the driver to feel uneasy. Improvements in riding comfort, driving controllability and stability are required particularly when the vehicle is traveling at high speeds.